1. Field of the Invention
This invention relates to a preconditioning process for a deposition chamber for the deposition of tungsten silicide on an active substrate. More particularly, this invention relates to a preconditioning process for treating surfaces of a deposition chamber, after a cleaning step and prior to deposition of tungsten silicide on an active substrate therein.
2. Description of the Related Art
In the deposition of a material such as a tungsten silicide on a substrate, residues from the deposition process, e.g., tungsten silicide residues, may also be deposited on the surfaces of the deposition chamber, including the chamber walls and the susceptor used to support the substrate in the deposition chamber. Repeated tungsten silicide depositions results in the buildup of such undesirable residues on the deposition chamber surfaces. To prevent such residues from flaking off the chamber surfaces, which would result in contamination of the substrate being processed in the chamber, the chamber is subject to periodic cleaning to remove such deposition residues. The removal of such tungsten silicide residues from the deposition chamber surface may be accomplished by the use of a fluorine-containing etchant such as NF.sub.3, or C.sub.2 F.sub.6, CHF.sub.3.
Normally, but not necessarily, the cleaning of the chamber is performed using a plasma in conjunction with such fluorine-containing etchant gases and may be followed by a passivation treatment with hydrogen to remove fluorine-bearing residues remaining in the chamber. However, in the subsequent deposition of tungsten silicide on an active substrate or wafer in the deposition chamber, after such a cleaning treatment, it has been found that the initial active substrate subsequently mounted on the susceptor is not adequately receptive to the deposition of a layer of tungsten silicide.
Thus, the tungsten silicide, deposited on the initial or first active substrate processed after cleaning, is of inferior quality and must be rejected. This, of course, is not only a rejection or loss of the cost of the tungsten silicide layer but also is a rejection or loss of any other structure previously formed on the active substrate, e.g., an integrated circuit structure created to that point on a semiconductor wafer. It will then be seen that the loss is not insubstantial. If the vacuum chamber is cleaned, for example, after every tenth wafer treated with tungsten silicide, the number of wafer rejected can amount to ten percent.
This problem is most apparent when a combination of a tungsten-bearing gas such as WF.sub.6 is used in connection with a chlorine-substituted silane gas such as dichlorosilane (DCS). Since the formation of a tungsten silicide layer using a chlorine-substituted silane gas has been found to provide step coverage over an uneven substrate surface superior to the use of silane itself, it is particularly important that a way be found to periodically clean the deposition chamber to remove undesired deposition residues without, however, interfering with subsequent depositions of tungsten silicide on active substrates, and in particular, without incurring the inferior deposition of tungsten silicide on the first or initial active substrate processed after such a cleaning of the vacuum chamber.
In our parent applications, Telford et al. Ser. Nos. 08/504,294, 08/352,265, and 08/083,420, we addressed this problem by proposing a pretreatment or conditioning to be carried out on an aluminum nitride surface of the susceptor in the deposition chamber after each cleaning operation, and prior to the processing of the first substrate after such a cleaning step. In particular, we taught a preconditioning treatment in which, after the cleaning of the deposition chamber, a deposition of tungsten silicide was carried out in the chamber, prior to mounting an active substrate on the susceptor, and using a combination of a tungsten-bearing gas such as WF.sub.6 ; a chlorine-substituted silane gaseous silicon source such as, for example, dichlorosilane (SiH.sub.2 Cl.sub.2), monochlorosilane (SiH.sub.3 Cl), or trichlorosilane (SiHCl.sub.3); and a carrier gas, such as argon or helium, i.e., the same gases used to form the desired tungsten silicide coating on substrate subsequently processed in the deposition chamber.
While this precoating or preconditioning procedure, as described and claimed in those parent applications, resulted in the subsequent formation of a satisfactory coating of tungsten silicide on even the first active substrate subsequently processed in the chamber after a cleaning step and this preconditioning step, it was found that in some instances, particularly when a chlorosilane was used in the preconditioning treatment, subsequent deposits on active substrates, e.g., after the processing of 10 or more active substrates, resulted in the eventual build up of residues on the chamber surfaces, including the susceptor surfaces, which tended to more readily flake off and form particles than previously deposited residues on the chamber surfaces.
We addressed this second problem, in our parent applications Telford et al. Ser. Nos. 08/364,022 and 08/138,179, by proposing that the preconditioning be carried out on the surfaces of the cleaned deposited chamber, including the susceptor, in a two step process carried out after each cleaning operation, and prior to the processing of the first active substrate after such a cleaning step. The two-step process described and claimed in parent Ser. Nos. 08/364,022 and 08/138,179 comprised first preconditioning the chamber surfaces with a mixture of a non-chlorinated silane and a tungsten-bearing gas, such as WF.sub.6, to form a first deposition of a silane-based tungsten silicide and then treating the already coated surfaces of the chamber in a second step with a mixture of a tungsten-bearing gas, such as WF.sub.6, and a chlorine-substituted silane, such as dichlorosilane (SiH.sub.2 Cl.sub.2), monochlorosilane (SiH.sub.3 Cl), or trichlorosilane (SiHCl.sub.3), to form a chlorine-substituted silane-based tungsten silicide deposition over the previous deposited silane-based tungsten silicide.